I have been to Bangkok many times, usually staying in a hotel in in the tourist areas of Sukhumvit or Silom. This time, as I was staying for a longer period of time (6 nights), I decided to try a different area.
Thongjuta's apartment is extremely convenient to the Huai Khwang MRT station, which is 4 stops from Sukhumvit and 8 stops from Silom. The apartment isn't large but it is very clean. My favorite part was, surprisingly, the great pool - many days I went there twice.
I also enjoyed exploring Huai Khwang, which is extremely local (compared to tourist areas). I ate lots of cheap and delicious street food for dinner from the local markets/street stalls.